The present invention relates to the contactless comminution of concrements in the body of a living being by means of shock waves which are focused onto the concrement.
A device of the type to which the invention pertains is, for example, shown in German printed patent application No. 3,312,014. A further improvement is disclosed in my copending patent application Ser. No. 802,720, filed Nov. 27, 1985. Among other features an electrical conductor arrangement is disclosed therein, having inductive properties owing to the configuration as a spirally shaped coil or as a coil wound from a flat ribbon. The coil is configured from an overall point of view, to have the shape of a spherical calotta. Upon feeding an electrical pulse into this coil, for example, on account of a capacitor discharge through a spark gap included in the circuit will produce a spark, so that a current pulse flows through the coil. A metal membrane faces the coil, but is separated therefrom by a thin electrical insulated layer and a current in opposite direction is induced resulting in a repulsion of the membrane from the coil. Since the membrane is in physical contact with an acoustic transmitting medium, shock waves are produced therein, and owing to the calotta shaped configuration of the membrane, these shock waves are focused. In order to avoid diffraction and reflection as it may occur at the housing part facing the membrane, I proposed in my co-pending application, to configure the zone into which the membrane emits the shock wave to be a truncated cavity filled with the transmission medium. Decisive here is a conical boundary of that medium delineating the focussing direction of the outermost beam portion.
Other known devices for the comminution of concrements operate with submerged spark gaps for the production of shock waves in the one focal point of an ellipsoid focusing the shock waves into the second focal point being situated to coincide with the concrement to be comminuted. Other devices for the generation of shock waves operate, for example, on the basis of piezoelectric effects or are constructed as magnetostrictive elements.
All these known devices require focusing of the shock waves but they all are constructed so that for physical reasons a negative pressure pulse wave cannot be completely avoided. Should these pressure drop pulses exceed a particular strength then the commensurate fucusing effect of this negative pressure pulse may also be particularly effective in the tissue of the living being be traversed and may lead to cavitation, i.e. to microscopic leasures and outright injuries to the tissue.